Schools are hiring out halls for weddings, sharing staff and setting up nurseries in attempts to raise cash, it has been suggested.
A new survey also indicates that some schools are expecting to restrict equipment, such as stationery, and cut trips in the future, in an attempt to save money.
The findings, based on a poll by The Key of more 1,000 school leaders, show that around a fifth (21.1%) believe they will need to make savings of between 2% and 5% of their expected costs in order to balance the budget in 2017/18.
A further 18.7% said their school would need to make savings of more than 8% and 17.6% said savings would need to be between 5% and 8%.
The poll found that more than two fifths (42.4%) said that they are letting buildings and facilities to generate income, while around one in four (24.5%) said that they were sharing contracts for services with other schools and a similar proportion (23.7%) are offering staff services to other schools and groups.
Schools are also taking measures such as building partnerships with local businesses and sharing curriculum resources with other schools, while 9.5% said they are setting up an on-site nursery and 4.4% are seeking donations from former pupils.
One primary school headteacher in Kent told the survey: "Schools have to look at themselves as businesses, the leaders as entrepreneurs who think creatively about what opportunities they can capitalise on.
"As well as setting up day-care provision and paid-for breakfast and after-school clubs, we also rent out our school hall most nights of the week for anything from church groups to weddings, birthday parties or language schools.
"All in all, our initiatives bring in between £200,000 and £300,000 a year and this gives us choices - choices that aren't made for us by government."
The poll also asked school leaders who have to make savings in 2017/18 what changes they expect to see.
More than two thirds (68.1%) said they expect a reduction in support staff and just under half (49.2%) said resources, such as pens and paper, are likely to be restricted.
Other measures schools expect to take include reductions in teaching staff, bigger class sizes and a narrower curriculum. A quarter (25.2%) said that they expect to see a reduction in extra-curricular activities, such as trips.
Fergal Roche, chief executive of The Key, said: "In every area, from staffing to stationery, school leaders are having to make difficult decisions about where to cut and restrict resources to balance their budgets, and it's clear they anticipate further financial challenges ahead.
"In the face of such challenges, entrepreneurial spirit and creativity abound in the solutions schools are finding to make the best use of their resources and generate additional income, and it's inspiring to hear so many accounts of staff and community going above and beyond to provide for their school."
Ministers have said that school funding is at record levels.
:: The survey questioned 1,182 school leaders online in February.
A Department for Education spokeswoman said: "The Government has protected the core schools budget in real terms since 2010, with school funding at its highest level on record at more than £40 billion in 2016-17 - and that is set to rise, as pupil numbers rise over the next two years, to £42 billion by 2019-20. But the system for distributing that funding across the country is unfair, opaque and outdated.
"We recognise that schools are facing cost pressures, which is why we will continue to provide support to help them use their funding in cost effective ways and make efficiencies.
"This includes improving the way they buy goods and services and our recently published school buying strategy is designed to help schools save over £1 billion a year by 2019-20 on non-staff spend.
"We know that some schools use their facilities to benefit the community and bring in additional revenue to benefit their students."
It is understood that schools have been hiring out facilities for years, as a way of generating extra income.